In a tape recorder, etc., it is required that a tape reel rotates at desired, predetermined rotation speeds to wind up a tape from a capstan without tape slack. However, irregular rotations of the reel sometimes occur because of various reasons.
Since the winding diameter of a tape reel is changed as a tape is progressively wound thereon, the length of the tape wound on the tape reel in one rotation thereof largely varies between a condition with no tape wound thereon and a condition with substially all length of the tape wound thereon. Therefore, a mechanism called friction arrangement is attached to a reel shaft in most cases, so that the friction arrangement slips under controls by the load applied to the reel in order to absorb the difference between different winding diameters and maintain a constant winding length per time.
In a cassette tape, etc., however, undulations are often produced on accumulated turns of a wound tape, and a hill portion of the undulations contacts the cassette half. This causes a so-called tight winding and increases the load. The increased load invites slipping motions of the friction mechanism which slows down the rotation and tape winding speed of the tape reel. When such tight winding occurs, a play run is difficult. That is, program changing operations are repeated, and this is dealt with as an abnormal inversion. Under such conditions, tape slack is produced in the tape subsequently supplied from the capstan, and this often invites such a trouble, among others, that the tape gets entangled on the capstan or the pinch roller.
Beside this, a conventional tape recorder, etc. is configured to merely detect a stationary condition of the tape reel to perform a channel changing or ejecting operation when the reel rotation is stopped upon arrival at a tape end. Therefore, it is impossible for the conventional tape recorder to early detect and cure the said abnormal rotation.